Signal portraying apparatus



Aug. 25, 1947. DOME 2,426,439-

' I SIGNAL PORTRAYING APPARATUS Filed 001;. 8, 1943 abmmsz SHIFT CIRCUIT SIG/VAL sou/ac:

Inventor: Robert B.Dom e,

by v His Attorney.

Patented Aug. 26, 1947 UNETED STATES ATEN PIC SIGNAL PORTRAYING APPARATUS Robert B. Dome, Bridgeport, Conn, assignor to I General Electric Company, a corporation of New York 11 Claims.

My invention relates to cathode ray signal portraying apparatus and particularly to such apparatus which is arranged to portray a plurality of signals simultaneously without interference between the several" signal circuits.

A cathode ray tube may be employed to portray two signals simultaneously by exciting the tube alternately with two signals and by arranging the deflection circuits so that the alternate signals appear on different portions of the surface of the fluorescent screen. Apparent persistence of the image on the fluorescent screen caused by the persistence of' vision makes the alternate signals appear as though they were being portrayed simultaneously. Various arrangements are provided for producing the alternate excitation butregardless of the arrangement it is essential that no interference occur between the alternate signals. Circuits which employ three-electrode electron discharge devices for amplifying the signals and for impressing them' on the deflection plates of the cathode ray tube inherently involve capacities, primarily the plate to'gridcapacity of the am plifying tube, through which signals may be coupled to the cathode ray deflection plates even though the grid of the tube-is biased beyond cutoff and-is nonconducting; Accordingly, it is an' object-bf my invention to provide a signal portraying'apparatus including acathode ray tube and circuits for alternately impressing a plurality of signals or deflection'waves on the electrodes of the cathode ray tube and including animproved arrangement for preventing interference'between the separatesignal circuits.

It is another object of my invention to provide a cathode ray signal portraying apparatus including signal amplifying circuits having three-electrode electron discharge devices and an improved-arrangement for preventing interference between the signals of the separate circuits due to coupling through the plate to grid capacities of the three-electrode devices.

The'features of my invention which I believe to be" novel are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation together withfurther objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawing in which Fig.1 diagrammatically represents one form of asignal portraying apparatus emboding my invention, and Fig. 2 represents the fluorescent screen of the cathode ray tube employed in the apparatus of Fig. 1.

The signal portraying apparatus illustrated in Figs 1 comprises a cathode ray electron discharge device {or tube provided with an electron gun'including a cathode H, a control electrode l2, a first anode I3 and-a second anode-l4 for producing an electron'beam within the tube. The beam produces'an image on the fluorescentscreen IS in a manner well-known in the art. In'order to utilize the electron beam for portraying a 'signaL pairs of vertical and horizon tal deflection electrodes or plates 16 and I! are provided. The *electron gun is provided with suitable operating potentialsfroma direct current source, such as a battery 20, and a voltage amplifiers are supplied with sine waves from' suitable sine-wave generators 26 and 21, the fre-- quency of the generator 21 being higher than that-of the" generator 26 for a purpose which will be explained below. In order to provide a" circular trace-as indicated in Fig. 2,' the sine' waves impressed on the verticaland horizontal plates are"niade out of phase. This-is accomplished by supplying si-ne waves fromthe generators 25 and 21 directly'to the amplifier '24 and through 90 phase'shift circuits 28 and 29* to the amplifier 25. A signal from an external source indicated at 30 is coupled through'a con denser 3l and resistance 32 to a signal point 33 in-the center of the fluorescent screen I55 Whena signal'pulse from thesource 30 is'impressed' on the point 33 the circular beam is deflected in accordance therewith. The vertical deflection amplifier '24 comprises twothree-electrode electron discharge devices35 and '36 having their control electrodes coupled to'th'e'sine wave generators 25 and 2T,respectively. Negative biasing means suchas batteries 31. and 38 are provided for maintaining a suitable low negative bias on the control electrodesof the devices 35 and 36 and a battery orother suitable source of greater negative bias indicated at 39 maybe connected selectively to either of the control electrodes of the devices 35 and 36 through a suitable switch indicated at 49. position indicated,'the control electrode of the device33isbias'ed negatively beyond cutofi so that the amplifier tube 36 is inoperative. In this position of the switch the deflection wave from the'generator 26"is amplified bythe device 35' and impressed across the deflection plates I6 through a coupling condenser 4| 'andresistance 42, a suitable source of anode potential such'as When" the switch Mlis in the a battery 43 being provided for the amplifiers 24 and 25. Amplifier 25 is similar to the amplifier 2G and comprises three-electrode electron discharge devices 45, 45 normally biasing batteries 4'] and 48, respectively, and cutofi biasing battery 49 arranged to be selectively connected to the control electrodes of the devices 45 and 45 through a switch 50 interlocked with the switch 45 so that the switches 49 and 5!] always connect the amplifiers 24 and 2'5 to a selected one of the generators 2'6 and 21. The output voltages from the anodes of the devices 45 and 45 are coupled to the horizontal deflection plates ll through a coupling capacitor 5| and resistance 52. In the position of the switch 50 illustrated, the generator 25 is connected to the amplifier tube 45 through the phase shift circuit 28, the tube 46 being biased beyond cutofl" by the battery 49. When the switches 40 and 50 are moved together to their upper positions the tubes 35 and 45 will be biased beyond cutoff and the high frequency deflection wave from the generator 2'! will be coupled to the tube 36 directly and to the tube 46 through the 90 phase shift circuit 29.

It will thus be evident that by changing the position of the switches 40 and 50 the deflection wave may be changed from the low frequency of the generator 26 to the higher frequency of the generator 21.

In the illustration of Fig. 2 the trace made by the cathode ray beam when the generator 25 is coupled to the deflection plates is indicated at 54 and the trace made by the generator 2'! is indicated at 55. In order to have both the traces 54 and 55 appear as though they were occurring simultaneously it is necessary to operate the switches 49 and 50 so that they connect the generators alternately at a rate sufliciently high that visually a trace made on the screen by a generator remains until the next trace is made, thereby giving the effect of continuous excitation. The switches 48 and 50 which have been diagrammatically illustrated as pole or knife switches are preferably electronic switches. The deflection plates to which the amplifiers 24 and 25 are coupled through the capacitors 4l'and 5|, respectively, are connected to the high voltage second anode I4 through resistors 58 and 51, respectively.

Thesignal traces as indicated in Fig. 2 comprise a low frequency trace and a higher frequency trace. In the illustration, for example, it is assumed that the trace 54 rotates once while the trace 55 rotates once for each indicated division of the scale for the trace 54. Trace 55 thus provides a Vernier reading for the scale 54 so that when a pulse is impressed on the point 33 by the signal source 30 it will appear, for example, at 58 on the trace 54 and at 59 on the trace 55, its position on the trace 55 indicating on a larger scale the distance of movement between the two adjacent markers on the scale for the trace 54.

It is evident that, for an accurate portrayal of the signal, interference between the defiection voltages of the generators 2'6 and 21 is objectionable and must be avoided. Such interference may occur due to the anode to control electrode capacities of the amplifier devices 35, ,36, 45 and 45. For example, when the switch 40 is in the position illustrated, a signal from the generator 21 may be coupled to thedeflection plates 55 through the grid to anode capacity of the tube tfieven though the tube is biased beyond 4 cutoff by the battery 39. I have found that interference due to coupling through the grid to anode capacities may be prevented by providing neutralizing condensers between the control grids of the amplifier devices and the deflection plates opposite the plates to which the cutoff amplifier tube is coupled.

I, therefore, provide variable condensers 50, 6| between the control electrodes of the devices 35 and 35 and the lower vertical plate l6 and variable condensers '62 and 53 between the control electrodes of the devices 45 and 45, respectively, and the left-hand horizontal plate ll. These variable condensers are adjusted so that their capacity is equal to the total grid to plate capacity of the respective amplifier tubes to which they are connected, it being understood of course that the total grid to plate capacity includes capacities of the leads associated with the anodes and the grids of these tubes. In addition to the neutralization of the anode to grid capacities of the amplifier tubes, I pro vide circuit components for making equal both the resistance and the capacity between ground or any suitable fixed reference potential and the two deflection plates of each pair of plates. For this purpose I provide resistors and 66 bypassed respectively by variable condensers 61 and 68 for connecting the lower potential plates of each of the pairs of plates I6 and I1, respectively to a point of fixed reference potential, i. e. to ground in the circuit illustrated. Bypass condensers 59, 10 and H bypass the resistors 22, 23 and 2! so that the resistors 65 and 6B are both connected to ground for alternating current at the frequencies in the range of frequencies impressed on the plates [6 and II. In order to make the resistance between the lower plate l6 and ground equal to the resistance between the upper plate l6 and ground the resistance 65 is made equal to the resistance of the parallel circuit including the resistances 42 and 56. In order to make the capacities to ground of the two plates equal, the condenser 67 is adjusted until I the capacity from the lower plate to ground is equal to the capacity from the upper plate to ground; the capacity of the upper plate to ground includes the plate to ground capacities of the tubes 35 and 35, the capacity of the wiring from the anodes to the upper plate and the capacity between the bulk of the coupling condenser 4l and ground. A similar adjustment is made in the resistance 66 and the capacity of the condenser 68 in order to make the capacity and resistance to ground from the left-hand horizontal plate I! equal to the capacity and resistance to ground from the right-hand plate I 7. V I

When the values of the condensers 60, BI, 62 and 53 and the adjustment of the parallel circuits including resistances 55 and 65 and condensers 61 and 58 are all made in the manner described, the separate plates of eachpair will be equally and oppositely energized by leakage through .the grid to plate capacities of the ampliference due to leakagefrom either source when the deflecting voltage is taken from the other source. Since the circuits between the deflecting plates of each pair and the fixed reference potential are balanced both for reactance and for resistance, the circuit is effective over a wide range of frequency.

WhileI have described my invention in connection with a particular type of deflection circuit and signal portraying system, other applications will readily be apparent to those skilled in the art. I do not, therefore, desire my invention to be limited .to the particular circuit arrangemeni; illustrated and described and I intend by the appended claims to cover all modifications in the spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. A cathode ray signal portraying apparatus comprising a cathode ray tube having a pair of cathode ray beam deflecting plates, two separate continuously operative deflection wave sources connected to energize said plates, means for rendering the connections between said plates and said sources selectively operative alternately to effect full energization of said plates from said sources alternately whereby leakage current tends to pass through the inoperative connection, and means for neutralizing the effect of leakage from said sources through said connections to said plates whereby interference with the wave from the selected source due to leakage through the inoperative connection is prevented.

2. A cathode ray signal portraying apparatus comprising a cathode ray tube having a pair of cathode ray beam deflecting plates, means including two separate sources of deflection waves for energizing said plates, each of said means having an electron discharge device including an anode and a cathode and a control electrode, means coupling both said anodes to one of said deflection plates for energizing said plates upon operation of either of said devices, means for rendering said devices operative alternately, and means for neutralizing the effect of leakage through the control electrode to anode capacities of said devices to said plates whereby interference with the wave from the operative device due to leakage through the inoperative device is prevented.

3. A cathode ray signal portraying apparatus comprising a cathode ray tube having a pair of cathode ray beam deflecting plates, one of said plates being connected to a point of fixed reference potential, two separate deflection wave sources coupled to the other of said plates for impressing deflection waves across said plates, means for rendering said sources operative alternately, means for neutralizing the effect of leakage from said sources to said plates, and means for making equal the reactances and the capacitances between each of said plates and said point .of fixed reference potential whereby interference with the wave from the operative source due to leakage through the inoperative source is prevented.

4. A cathode ray signal portraying apparatus comprising a cathode ray tube having an electron gun and a pair of cathode ray beam deflecting plates, means including an electron discharge device having an anode and a cathode and a control electrode for impressing a deflecting voltage across said deflecting plates, said anode being coupled to one of said plates and said cathode and the other of said plates being connected to a point of fixed reference potential, and means providing capacitance connected between said control electrode and said other plate for neutralizing the control electrode to anode capacity of said device.

5. A cathode ray signal portraying apparatus comprising a cathode ray tube having an electron gun'and a pair of cathode ray beam deflecting plates, means including an electron discharge device having an anode and a cathode and a control electrode for impressing a deflecting voltage across said deflecting plates, said anode being coupled to one of said plates and said cathode being connected to a point of fixed reference potential, means connecting said control electrode and the other one of said plates for neutralizing the control electrode to anode capacity of said device, and means connecting said other plate to said point of fixed reference potential for making equal the impedances between each of said plates and said point of reference potential.

6. A cathode ray signal portraying apparatus comprising a cathode ray tube having an electron gun and a pair of cathode ray beam deflecting plates, means including an electron discharge device having an anode and a cathode and a control electrode for impressing a deflecting voltage across said deflecting plates, said anode being coupled to one of said plates and said cathode being connected to a point of fixed reference potential, means connecting said control electrode and the other one of said plates for neutralizing the control electrode to anode capacity of said device, and means including a resista n ce for connecting said other plate to said point of fixed reference potential, said resistance having a value such that the paths between each of said plates and said point of reference potential have the same resistance.

'7. A cathode ray signal portraying apparatus comprising a cathode ray tube having an electron gun and a pair of beam deflecting plates, means including an electron discharge device having an anode and a cathode and a control electrode for impressing a deflecting voltage across said deflecting plates, said anode being coupled to one of said plates and said cathode being connected to a point of fixed reference potential, means connecting said control electrode and the other one of said plates for neutralizing the control electrode to anode capacity of said device, and means for connecting said other plate to said point of reference potential and for making equal the capacitances between each of said plates and said point of reference potential.

8. A cathode ray signal portraying apparatus comprising a cathode ray tube having an electron gun and a pair of cathode ray beam deflecting plates, means including an electron discharge device having an anode and a cathode and a control electrode for impressing a deflecting voltage across said deflecting plates, said anode being coupled to one of said plates and said cathode being connected to a point of fixed reference potential, means connecting said control electrode and the other one of said plates for neutralizing the control electrode to anode capacity of said device, and means including a resistance and a condenser in parallel for connecting said other plate to said point of fixed reference potential and for making equal both the resistance and the capacitance between each of said plates and said point of reference potential.

9. A cathode ray signal portraying apparatus comprising a cathode ray tube having an electron gun and a pair of beam deflecting plates; means including an electron discharge device having an anode and a cathode and a control electrode for impressing'a deflecting voltage across said deflecting plates, said anode being coupled to one of said deflecting plates; means for connectin the other of said plates to a point of fixed reference potential, and means for neutralizing the effect of leakage through said device to prevent undesired deflection of the cathode ray beam, said neutralizing means comprising a firstcondenser connected between said control electrode and said other plate and a second condenser connecting said other plate to said point of reference potential; said first condenser having a capacity equal to the control electrode to anode capacity of said device and the capacity of said second condenser being selected so that the same value of capacity exists "from each of said plates to said point of reference potential;

10. A cathode ray signal portraying apparatus comprising a cathode ray tube having an electron gun and a pair of beam deflecting plates, means including an electron discharge device having an anode and a cathode and a control electrode for impressing a deflecting voltage across said defleeting plates, said anode 'being coupled to one of said deflecting plates, means including a resistance for connecting the other of said plates to a point of fixed reference potential, said resistance having a value such that the resistance is the same between both said plates and said point of reference potential, and means for neutra liziirig the efiect of leakage through said device to prevent undesired deflection of the cathode ray beam, said neutralizing means comprising a first condenser connected between said control electrode and said other plate and 'a-second condenser shuntingsaid resistance, said first condenser having a capacity equal to the control electrode to anode capacity or said device and the capacity of said second condenser being selected so that the same value of capacity exists from each of said plates to said point of reference potential.

11. A cathode ray signal portraying device comprising a cathode ray tube having a pair of cathode ray beam deflecting plates, two separate deflection wave sources, means providing respective separate electron discharge paths for connect-ing saidsources to energizesaid plates, means for rendering said electron discharge paths 0perative alternately, and means for neutralizing the effect -of leakage from said sources to said plates whereby interference with the wave from the operative one of said paths due to leakage through the inoperative path is prevented.

ROBERT B. DOME.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,208,379 Luck 1 July 16, 1940 Re. 20,945 Bedell 1 -6-. Dec. 1-3, 1938 2,089,430 Boys et a1. 1 Aug. 10, 1937 2,312,761 Hershberger Mar. 2, 1943 2,146,862 'Shumard Feb. '14, 1939 2,313,966 Poch Mar. 16, 1943 

